The present invention relates to a slip-controlled brake device for automotive vehicles with a hydraulic pressure generating arrangement which is, via a pneumatically actuated pressure modulator, connected to at least one hydraulic wheel cylinder brake circuit. The pressure modulator comprises a vacuum power generator and a compensating cylinder equipped with a hydraulic piston connected with the piston wall of the vacuum power generator which wall is pre-loaded into the inoperative position by means of a return spring. The compensating cylinder's compensating chamber communicates with the wheel cylinder brake circuit, and a higher pressure is temporarily applied to the piston wall of the vacuum power generator in the direction which increases the volume in the compensating chamber. A normally open isolating valve is located in the connecting line between the pressure generating arrangement and the compensating chamber. When a brake slip signal derived from a brake slip control circuitry occurs, the piston wall is normally supplied with a vacuum on both sides and the isolating valve is closed.
In my copending application U.S. Ser. No. 944,242 filed Dec. 18, 1986 (German printed and published patent application No. 35 45 236), independent vacuum power generators are provided for brake power boosting and pressure modulation. In order to relieve the connected wheel cylinder brake circuit and/or the connected wheel cylinder brake circuits in the event of a brake slip control action, electromagnetically actuated opening valves are arranged between the pressure modulator and the wheel cylinder brake circuit.